Mix sugar and cocoa together in saucepan, Stir in milk, Add butter, Cook over low heat and stir until butter melts, Continue to cook over low heat until mixture comes to a rapid boil, Cook 3 minutes more, Remove from heat,______, Place pan in cold water and continue to stir until it begins to thicken, Pour over 9 x 13 cake in which holes have been punched with a toothpick, fork or skewer,